1 IntroductionAvoiding Condensation Problems

MAINTENANCE MATTERSBuilding Maintenance Bulletin

Avoiding Condensation Problems Have you ever noticed water droplets on your window or black

staining on the drywall of your walls? Have you ever wondered

why the moisture returns around your windows after you have

wiped it away? This type of moisture is from the interior air and

is commonly referred to as condensation.

What is Condensation and How Does it Form in My Home?

Condensation occurs in your home when moist air comes into contact with

a surface which is at a lower temperature. Moist air contains water vapour —

commonly referred to as humidity. Indoors, we can increase humidity through

our activities and lifestyle. If a surface in your home is cold enough, the air in the

immediate vicinity of the surface will be cooled, sometimes causing the moisture

in the air to condense or change into a liquid on the surface.

Condensation forms first on the coldest surfaces of a room, usually on glass

surfaces of windows and doors. These surfaces are typically cooled by lower

exterior temperatures during the winter months much

more easily than the walls which are kept warm by

insulation. For example, if it is cold enough outside

and/or warm and humid enough inside, condensation

may occur on or around your windows resulting in

fogging, water or ice on the windows themselves or even

a puddle of water on the window frame or sill. Other

examples of condensation in your home can include

damp spots or mildew on outside wall corners, closet

walls or baseboards. Areas of your home with poor air

circulation, such as behind furniture or in a cupboard or

closet, can also be susceptible to condensation.

February 2018

MAINTENANCE MATTERS

Number 3

1

Condensation forms first on the coldest surfaces of a room, usually on glass sur-faces of windows and doors.

Maintenance MattersThis series of bulletins and

companion videos is designed to

provide practical information on

maintaining residential buildings.

Produced by BC Housing, in

collaboration with Polygon and

Canada Mortgage and Housing

Corporation, this bulletin was

prepared by a consortium of

building envelope experts.

Use your kitchen exhaust fan or range hood to remove humidity generated by cooking. The exhaust fan should be vented to the outside.

1 Introduction

2 Maintenance Matters No. 3

Avoiding Condensation Problems

A small amount of condensation appearing on a surface

may not necessarily be a problem. It depends on the

amount of moisture that forms, how long it stays, and

whether it accumulates on surfaces that can be damaged

by water. Condensation can be short-term during a severe

cold spell, or occur in a localized area such as kitchen,

bathroom or laundry room.

In many instances, condensation moisture simply

evaporates back into the air once the surfaces warm up

or the moisture source is reduced. An example of this is

moisture that condenses on a bathroom window during

a shower and quickly disappears shortly after the shower

is turned off. However, as a general rule, steps should be

taken to avoid condensation problems wherever possible

as moisture can lead to damage.

Why Must I Avoid Condensation Problems?

Condensation can cause serious damage to the interior

and structural elements of your home or building.

If condensation occurs frequently enough and for

prolonged periods of time, materials in contact with the

moisture may be damaged. Drywall and wood finishes

around windows are two examples of materials in your

home that can readily absorb moisture and become

damaged if they remain wet for a sustained period of

time. If left unchecked, condensation problems can cause:

• crumbling or soft spots in drywall

• decay in wood framing or corrosion of steel framing

• peeling paint

• damage to the insulation inside the walls

• mould and mildew problems in your home

Most importantly, taking preventative steps to avoid

condensation from occurring in your home will help

prevent avoidable and expensive problems in the future.

Sources of Moisture in the Home

We add to humidity levels in our home through our

activities and lifestyle. Water vapour is added to the air

in large quantities by our breathing and perspiration,

cooking, bathing, cleaning and other daily activities.

How we produce humidity in our homes

• A family of four can add moisture to the air

equivalent to 30 to 40 litres of water per week

• Showering, cooking, bathing and washing can

add 15 to 20 litres per week

• Drying clothes indoors can add 10 to 15 litres

per week

Source: Natural Resources Canada

Newly constructed homes may temporarily exhibit a

higher potential for condensation as moisture in plaster,

cement and other building materials escapes into the

air during the first heating season. This elevated level

of moisture in the air should taper off after a month or

two. If it doesn’t, you should inform your building or

maintenance manager of the situation.

Evidence of problems resulting from condensation can be seen on the interior window sill.

Condensation has led to mould problems on the drywall.

Maintenance Matters No. 3 3

1 IntroductionAvoiding Condensation Problems

What Should the Indoor Temperature and Humidity Levels be?

Interior temperature and relative humidity is often a matter of personal preference, but exceeding recommended humidity levels for extended periods of time can lead to a higher risk of condensation problems in your home. The recommended relative humidity level varies between winter and summer, and by location.

As a rough “rule of thumb,” interior air temperatures should generally be maintained between 18°C and 24°C with relative humidity falling between 35% and 60% for the coastal temperate climate regions of British Columbia during the winter months. In colder and drier regions of the province, interior humidity levels should be limited to between 25% and 40% during the winter months. If you are unsure of the relative humidity in your home, small devices called “hygrometers” can be purchased that will allow you to measure the humidity levels.

Humidity cannot be eliminated from the air altogether. It is needed to maintain a comfortable and healthy interior environment. Without humidity we would suffer from chapped lips and dry skin, sore throats, breathing problems, static electricity, and damage to equipment and furniture. However, if humidity gets too high, problems will arise in your home such as condensation, musty smells, mould growth, allergic reactions and damage to walls and interior finishes.

How do I Avoid Condensation Problems?There are number of steps that you can take to prevent condensation problems from occurring in your home.

1) Reduce the amount of moisture or humidity generated in your home

• Do not regularly hang large amounts of clothes to dry indoors. Wherever possible, dry your clothes in a dryer with an outside vent.

• Shut off the humidifier if you are using one.

• While cooking, put a lid on boiling water — it will also

boil faster!

• Try to have shorter showers. You will save energy

required to heat the water and conserve water.

• Ensure the lint trap in your clothes dryer is clean.

The lint trap should be inspected and cleaned before each use.

• As much as possible, try to wash full loads of dishes in the dishwasher.

• Do not store wood for your fire place indoors.

2) Promote good air circulation in your home

• Open blinds and drapes so that air can circulate freely over the windows.

• Direct heat towards exterior walls and windows.

• Where condensation at window sills is a persistent problem, remove any objects on the window sill such as books, photographs, and knickknacks as they prevent air from circulating and removing the moisture.

• Move furniture such as sofas and bookcases so they are not touching outside walls. This will improve air circulation around the cooler outside wall and reduce condensation potential.

3) Promote good ventilation in your home

• Use the kitchen exhaust fan or range hood to remove humidity generated by cooking.

Note: the exhaust fan or range hood should be vented to the outside.

• Use bathroom fans and humidistats (if you have one) while bathing or showering. Some bathroom exhaust fans are connected to a humidistat that can be preset to ventilate the room when the humidity reaches a certain level, and keep the fan running until the humidity is below that set point. It is important that humidistats be set to the appropriate level and not turned to “off.” If the bathroom does not have a humidistat, the exhaust fan should be left running for a period of time after bathing or showering to remove the excess moisture from the bathroom. The exhaust fan should be vented to the outdoors.

1 Introduction

4 Maintenance Matters No. 3

Avoiding Condensation Problems

• Some newer homes have a pre-set principal

exhaust fan. Ensure that this fan is set to run for

two 4-hour periods per day.

• Open windows periodically and ensure that fresh

air intake vents are not blocked.

• Make sure exterior vent hoods for your dryer,

bathroom and kitchen vents are unobstructed and

operating freely. Clothes dryers that take longer

to dry than usual, and kitchen or bathroom fans

that seem to not move the air could be signs of some

obstruction in the duct or the outlet. Keeping vent

hoods and lint traps clear will also reduce the

amount of energy required to dry the clothes, thus

reducing utility bills. Qualified professionals should

be used to carry out this maintenance item.

• Consider upgrading your kitchen or bathroom fans.

If you feel that your kitchen or bathroom fans make

noise, but don’t seem to do anything, you may be

right. Some older or cheaper units may not work

effectively and tend to be noisy. A simple upgrade

is relatively inexpensive and will often dramatically

improve performance. Look for units with high air

movement measured in cubic feet per minute (cf/m)

or litre per second (L/s), and a low noise rating

measured in decibels (dB) or sones.

In most cases you can address high humidity and

condensation through reducing the amount of humidity

generated in your home. Ventilation may only reduce

humidity levels if the air introduced into the room is drier

than the interior air. When ventilation is not effective

at lowering the humidity sufficiently, you may need to

incorporate the use of a dehumidifier (or air conditioner)

to further reduce humidity levels. However, this should be

considered as a last resort after you have taken necessary

steps to reduce the amount of humidity generated in your

home. Also, dehumidifiers require electricity to operate and,

therefore, may be an expensive option.

Dealing with Persistent Condensation Problems

Condensation is usually a localized problem that you can

address by taking the steps described above to reduce

the humidity or to promote good air circulation and

ventilation in your home. However, if you have taken

these steps and continue to experience condensation

problems, other problems may exist that are more

appropriately addressed by your maintenance manager

or a qualified professional. Symptoms related to

persistent condensation problems include:

• windows that continue to have water droplets or that

fog up, frost or get ice build-up, even after you have

taken necessary steps to lower humidity levels and

prevent condensation in your home

• black staining on the inside of walls, mainly in corners

and near the floor or ceiling

• mould or mildew growth

• ice or frost under roof sheathing boards

• delamination of plywood materials

• damp or moist basement walls or floors

Report persistent condensation problems to your

maintenance manager. Persistent condensation problems

may relate to air leakage in your home, typically at the

base of the wall, (sometimes causing black staining at

carpet edges) or at electrical lighting and receptacle

outlets, and around windows1 and doors. This air leakage

can allow cold air into the wall assembly and thus cool

the wall and increase the potential for condensation. In

other cases, it may be necessary to bring warm air to cold Use bathroom fans, and humidistats if you have one, while bathing or showering.

1 IntroductionAvoiding Condensation Problems

surfaces, either by changing the building’s heating patterns

or by providing dedicated heat sources to problem areas.

Blowing warm air at problem areas has the additional

effect of encouraging evaporation at the problem

location. In some cases the solution may be to insulate

surfaces against cold temperatures, usually by increasing

insulation levels in the walls behind the problem areas.

The solutions to each of these potential problems,

however, must be carried out by qualified professionals

and co-ordinated by your maintenance manager.

1 In some climates, such as central and northern British Columbia, a historical remedy for condensation around windows was to open the window slightly to allow the very dry outdoor air to mix with the relatively humid indoor air and reduce the potential for condensation. This approach is NOT recommended as it can result in condensation and serious damage in parts of the wall that are not visible to the occupants. It also results in a large consumption of energy.

Action Plan Tips

• Take steps to avoid condensation problems in your

home:

• Reduce the amount of moisture or humidity

generated in your home. For example, do not hang

laundry to dry indoors and take shorter showers.

• Promote good air circulation in your home. For

example, open blinds and drapes and move furniture

so that it is not touching an outside wall.

• Promote good ventilation in your home. For

example, use kitchen exhaust fans, bathroom fans

and humidistats as well as consider upgrading your

exhaust fans if they are performing poorly.

• If a persistent condensation problem becomes evident

(after taking the above steps), notify your maintenance

manager. A qualified professional may be needed to

address the underlying cause of this problem.

More Information

› Moisture Problems: Why Should I Worry About Moisture Problems?, available at www.oee.nrcan.gc.ca

› Building Enclosure Design Guide – Wood-Frame Multi-Unit Residential Buildings, available at www.bchousing.org

› See your building’s maintenance manual

› Subscribe to receive Maintenance Matters bulletins at www.bchousing.org

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ousing

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Notice to ReadersThis bulletin is intended to provide readers with general information only. Issues and problems related to buildings and construction arecomplicated and may have a variety of causes. Readers are urged not to rely simply on this bulletin and to consult with appropriate and reputa-ble professionals and construction specialists before taking any specific action. The authors, contributors, funders, and publishers assume no liability for the accuracy of the statements made or for any damage, loss, injury or expense that may be incurred or suffered as a result of the use of or reliance on the contents of this bulletin. The views expressed do not necessarily represent those of individual contributors or BC Housing.The regulations under the Homeowner Protection Act contain specific

provisions requiring owners to mitigate and restrict damage to their homes and permitting warranty providers to exclude coverage for damage caused or made worse by negligent or improper maintenance. These apply to both new and building envelope renovated homes covered by home warranty insurance. Failure to carry out proper mainte-nance or carrying out improper maintenance either yourself or through qualified or unqualified personnel may negatively affect your warranty coverage. It is important for the property owner to read and review their warranty documents to understand how to file any claims and correspondence in the proper written form directly with the warranty company. Refer to your home warranty insurance documentation or contact your warranty insurance provider for more information.